Dispenser containers for viscous fluids are well known. For example, a dispenser for viscous cosmetics such as toothpaste or lotion is described in Kolaczinski et al., U.S. Pat. No. 4,154,371. The Kolaczinksi et al. container comprises a piston forming the bottom of the container and beind displaceable in the container; a compressible container part, lying in front of the piston, a mouthpiece, for withdrawal of the contents, of flexible and elastic material; and a delivery valve opening on excess pressure in the container. The piston is secured by a blocking pawl against any displacement causing enlargement of the interior space of the container. The delivery valve comprises a flap having an area of 0.8 cm.sup.2 or less which is mounted in the mouthpiece by resilient hinge means.
A similarly useful dispenser is also described in Spatz, U.S. Pat. No. 3,361,305. The piston of the dispenser described, which piston effectively pushes out the container filling, does not require a locking means, for example, catches or ratchets, against displacement due to internal displacement or pressure in the container since, when the diaphragm pump is operated, either its inlet valve or its outlet valve is always closed and the material is introduced into the pump chamber by vacuum.
In the Spatz dispenser, several flap valves are arranged in the top surface of the container between the storage chamber of the container and the pump chamber, which flap valves are arranged substantially symmetrically to the center of the top surface. While the flap valve openings consist of holes whose surface is slightly inclined to the inside from the edge to the center of the top surface, the respective flaps are a part of a plate arranged in the pump chamber on the top surface. When the diaphragm pump of the dispenser is operated, a flexible, elastic surface is moved downward, perpendicularly to the top surface containing the flap valves in such a way that the product contained in the pump chamber is ejected or dispensed through the delivery valve of the dispenser. When the flexible, elastic surface returns to its normal, unstressed position, the delivery valve is closed because of a resulting vacuum and the inlet flap valves arranged in the top surface open in such a way that new material is drawn into the pump chamber from the interior of the container, that is, from the storage chamber, by the pressure differential, or vacuum, produced in the pump chamber.
A disadvantage of the arrangement characteristic of the Spatz device is that the flaps of the valves arranged in the top surface must be moved when the valve opens or closes exactly either in the direction of flow or opposite to the direction of flow of the product from the interior of the container into the pump chamber. The closing of the inlet flap valves as well as the opening of these valves is therefore slightly delayed, relative to the corresponding lifting phase of the diaphragm pump, in such a way that the pump chamber is only partly emptied when the product is ejected or dispensed and only is partly filled when the product is drawn in. Not only does this make operation of the pump and of the dispenser relatively difficult but also the dosing accuracy of the dispenser suffers.